1. Field of the Invention
This invention relates to a load control apparatus for use in an image forming apparatus, such as a copier, a facsimile, a printer and a hybrid machine having a plurality of functions of the image forming apparatus, and in particular, relates to a load control apparatus capable of avoiding damage to a load of the image forming apparatus.
2. Discussion of the Background Art
A variety of technologies have been developed that avoid damage to a load, such as a motor and so on, by stopping the load in an emergency to keep the load operating safely. For example, the below-described technologies are well known.
As described in the Japanese Laid Open Patent Publication No. 5-286642, a sheet cassette in an image forming apparatus is moved by a motor between a setting position and a removing position. A sensor is provided to detect an obstacle that may exist between the setting position and the removing position. The motor is controlled to stop driving when the sensor detects the obstacle.
Further, as described in the Japanese Laid Open Patent Publication No. 5-304718, a sensor is provided to measure an amount of current. The sensor outputs a signal when a current larger than a rated current flows. A message or a mark indicating an overload state is displayed when the signal is output. A current fuse is then promoted to melt down, since the current flow is amplified through a safety circuit which avoids problems from occurring with parts of the motor.
Further, as described in the Japanese Laid Open Patent Publication No. 6-6996, a sensor is provided to detect a reverse revolution of a motor that drives a reciprocating device. The sensor outputs a signal when the motor does not revolve in a reverse direction within a prescribed time period after the reverse revolution is commanded. The motor is controlled to stop when the sensor does not output the signal.
In recent years, a plurality of motors, such as stepping motors, are increasingly employed in an image forming apparatus and so on. A base plate that supports the stepping motor is directly mounted on mold parts of the image forming apparatus. Thus, if for some reason the stepping motor is supplied with power for a long time, the stepping motor may generate heat, thereby having an abnormally high temperature. As a result, the mold parts may melt and become deformed. Further, the operational safety features required of the stepping motor may be lost.
In addition, if a central processing unit (hereinafter referred to as a CPU) of a microcomputer of the image forming apparatus controls a plurality of stepping motors by itself, almost all of the operations of the CPU are occupied by control operations for the stepping motors. Thus, a hardware circuit, such as an application specific integrated circuit (hereinafter referred to as an ASIC) has sometimes been recently employed to control the stepping motor for the CPU.
In a case of using such an ASIC, no problem occurs when a prescribed allowable amount of power supply voltage is applied having an alternating current (hereinafter referred to as AC), for example, which is more or less 15 percent of a rated voltage for the case of a copier.
However, if a plurality of copiers employing the ASIC are connected to an AC power supply constituted by one circuit, electrical power lower than the prescribed allowable range may be supplied to each of the copiers. Accordingly, a voltage, which is outside the allowable range, may be applied to the microcomputer and the ASIC. As a result, the microcomputer and the ASIC sometimes operate in an unexpected manner. For example, the ASIC may unexpectedly continue to output signals for driving the stepping motor.